"Joel Kolstad" bravely wrote to "All" (23 Oct 05 20:26:37)
--- on the heady topic of "Wideband RF blocking"


Add series or/and parallel resistance to dampen the resonances.

A*s*i*m*o*v


JK From: "Joel Kolstad"
JK Xref: core-easynews rec.radio.amateur.homebrew:88454

JK In a receiver, for wideband (10-150MHz) biasing of a MMIC amplifier
JK using inductors between the RF trace and the power rails, I'm finding
JK that a single inductor tends not to work so well due to (1) wanting a
JK largish inductor (say, one with 500 ohms of reactance at 10MHz in a 50
JK ohm system -- 8uH) but (2) not going beyond the self-resonant
JK frequency of the inductor, which of course is smaller the larger the
JK inductance (that 8uH inductor might typically have an SRF of 50MHz,
JK noticeably below the 150MHz I'm trying to achieve RF blocking to!).

JK Is there a better means of providing wideband DC biasing/RF blocking
JK than just placing a large and small inductor in series? I've run
JK SPICE simulations of this, and -- just as when you stack multiple
JK capacitors in parallel for wider RF coupling -- there are significant
JK anti-resonances that drop the overall reactance of the pair of
JK inductors to much less than 500 ohm (even less than 50 ohms!) unless
JK you're very careful in the choice of individual inductor SRFs,
JK inductances, etc.
JK Thanks,
JK ---Joel Kolstad

.... Why do we park on driveways and drive on parkways?